There is an increasing demand for transparent antennas that can be attached to non-traditional surfaces and materials, such as conformal antennas adhering to flexible fabrics and plastic substrates. Antennas meeting these needs have previously been prototyped through the use of conductive inks on inflexible substrates. However, while highly conductive, these ink antennas are not optically transparent and do not adhere reliably on flexible substrates.
Optical translucence allows for the potential to hide an antenna or to make the antenna virtually invisible when mounted on a transparent substrate, such as a vehicle's windshield. While conductive polymers have lower conductivities in comparison to traditional antenna materials and conductive inks, they have many advantages such as their low cost, ease of processing, and potential for all-additive ink-jet manufacturing. Previously reported conductive polymer antennas used polymers that included silver particles or were made from polymers that needed to be thick in order to achieve high conductivity. However, these previously reported antennas were neither transparent nor flexible.
Fabrication of translucent conformal antennas utilizing additive printing methods offers a stark contrast to traditional subtractive fabrication techniques generally used in circuit board and RF production, such as milling and chemical etching. As an additive process, printing can achieve patterns and geometries while using a minimum of material, which poses a large economic advantage especially when printing precious metals or other high cost materials. The additive nature of the process also allows for the use of a wide array of substrates including traditional boards such as FR-4 and ceramic-based dielectric materials. The low-temperature and non-contact nature of the process also allow for the use of many non-traditional and less rigid substrates such as plastics, polymers, fabrics, and paper.
Radio frequency identification (RFID) is a very popular technology for an increasing number of applications. The most basic passive RFID tag system consists of an interrogator (an infrastructure used to query tags) and the tags themselves. The core technology is the backscattering technique that enables very inexpensive circuits without batteries to return information to an interrogator. Because of the simplicity of the optically transparent printed conformal polymer antenna, the RFID tags can be made smaller and less expensive.
Previous work has focused on creating antennas that provide good matching and high efficiency for RFID systems. Examples of these designs include meandering dipoles, which reduce the total length of the dipole antenna by bending the two poles. Non-traditional (silver-ink) materials have been used before for RFID applications due to their low cost. However, they are not as flexible, conformal, nor as transparent as conductive polymers. Conductive polymers have been used for very low frequency applications, but due to their low conductivity have only recently been used for radio frequency (RF) applications. There are now conductive polymers that have high enough conductivity at RF frequencies to make them suitable for RFID applications. Methods are desired for using such conductive polymers to create antennas for RFID and other wireless communications applications.